Sunderland manager Chris Coleman has confirmed that Duncan Watmore has undergone knee surgery and will "probably" not play this season.
The 22-year-old only returned to action in September after missing the second half of last season with a cruciate injury.
However, Watmore had to be taken off during the 2-2 draw with Millwall on Saturday after picking up an injury to the same knee that he damaged in December last year.
New Black Cats boss Coleman told a press conference on Thursday: "This season probably won't happen for him. I told Duncan on Sunday, 'if it's bad news then the worst thing you can do is put a time on it', but he'll be chasing time as he'll want to be back.
"Life is frustrating sometimes as he's desperate to play football and desperate to play for Sunderland. He's worked so hard to get back, he's such a bright player, so to lose a player like him was a big blow to everybody.
"He had surgery today so it's as we feared and it'll be another long one for him, but forget me and forget us, he's a young man with a real good career ahead of him and he's a good guy who loves his football. He'll be devastated and we have to take care of him, however long it takes. He'll be back, I'm sure about that."
Watmore has made 49 appearances for Sunderland's senior team, scoring four goals and recording seven assists.
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